BitowN — Note on the Decay of Magnetism in Bar Magnets. 81 



Section 2. 



In February, 1910, the writer read a paper before this Society on " Chrome 

 Steel Permanent Magnets," where results were given for seven magnets of 

 dimension-ratio 33, the magnets containing different percentages of chromium.^ 

 They were then tested for magnetic moment per granmre wlien in the 

 condition (1) glass-hard, (2) annealed, and also tested for the percentage loss 

 in the moment due to percussion. The del ails of the tests and the heat- 

 treatment of the magnets are given in the paper referred to. The magnets 

 in the annealed state were put carefully away after the tests, and have 

 remained undisturbed from that date to this, or about ten years, when they 

 have again been tested for the decay of magnetism, with the results here 

 given. 



In Table III the results in column A are the values of the moments 

 when the magnets were stored away ten years ago, that is, they are the 

 values given in the paper referred to above, minus the percentage loss due to 

 percussion in each case. 



Table III. 



A = Magnetic moment per gramme in Januiiry, 1910. 



B= „ ,, ,, „ 1920. 



C= Percentage loss in the moment for a period of about ten years. 



D = Total percentage loss due to percussion from previous paper, p. 351. 



It has been stated by Mme. Curie that small quantities of silicon have 

 little or no effect on the magnetic properties of a magnet.^ 



' Scient. Pioc. Roy. Dub. Soc, April, 1910, vol. xii, pp. 349-353. 

 ^ Bull, de la .Societe cl'Encouragement, pp. 36-76. 



